The present invention relates to a horizontal sync pulse control circuit for a PCM signal recording and reproducing apparatus which utilizes at least in part a video tape recorder (will be termed VTR hereinafter) for recording and reproducing a PCM signal conformable to the television signal standard.
Common PCM signal recording and reproducing apparatus are designed to utilize at least in part VTRs for recording and reproducing PCM signals conformable to the television signal standards respectively.
The PCM signal recording and reproducing apparatus referred to herein is of the type which modulates analog audio signals to PCM signals conforming to television signal standards, records the PCM signals on a VTR tape by means of a VTR head, modulates the PCM signals reproduced from the VTR tape into the analog audio signals, and reproduces the analog audio signals. In such an apparatus, a scratch or a piece of dust on the recording medium, i.e., the VTR tape, causes a dropout of record, giving rise to an erroneous reproduction of the signal. When errors occur in the reproduced data signal within a certain degree of probability, they can be retrieved perfectly by use of error correction bits, as is known in the art, and there is no practical problem. However, if an error occurs on the synchronizing (sync) signal, there is no way to retrieve it, resulting in a failure of synchronization in the PCM signal processing circuit and thus in generation of noise. In the PCM signal recording and reproducing apparatus of this type, data is rearranged in time by the interleaving operation in recording, and the original arrangement is restored by the de-interleaving operation in reproduction. In this case, when the horizontal sync signal is disturbed, it fails to maintain the correct timing relationship with the PCM data signal, resulting in a failure of reproduction for the data signal during the period of 245 horizontal sync signals. In consequence, substantial noise is created in the de-interleaving operation and the error correcting operation for the data signal.